Osteoid osteomas are benign bone-forming tumors that typically occur in children (particularly adolescents) frequently affecting long bones [1]. Osteoid osteoma accounts for 0.3% of all primary bone tumors [2,3]. It can affect any bone in the body, spine is involved in 10% of cases, with lumbar spine being most common site and usually occur mainly posterior elements, such as spinous processes, transverse processes, facets, laminae, and pedicles [4]. Osteoid osteoma of cervical spine is a rare clinical entity and accounts for 4% of cases of overall spinal osteoid osteoma [5].

Structurally, osteoid osteomas contain osteoblasts that produce immature bone tissue. Histologically, the lesion produces osteoid and consists of compact (woven) bone with interconnecting trabeculae surrounding a central nidus of osteoid. They are usually small, benign, and self-limited with local production of prostaglandin [6]. The most common clinical presentation is pain localized to the site of the lesion [7,8].

Computed tomography (CT) and magnetic resonance imaging (MRI) are very helpful in making a diagnosis. Radiographically, it appears as a small radiolucent lesion or a nidus <15 mm in diameter and is characterized by a central nidus surrounded by a sclerotic reactive bone, comprising osteoid, osteoblasts, and fibrovascular stroma [9,10].

Treatment is usually conservative, but if symptoms persist despite conservative management, surgical excision may be considered. Various surgical methods such as open excision and radiofrequency ablation (RFA) have been used [11]. In recent years, several studies have reported the removal of cervical osteomas using a microscope [12-15].

Recently, surgeries using unilateral biportal endoscopy (UBE) have been reported for the removal of cervical epidural tumors [16]. There is a case of thoracolumbar osteoid osteoma removal performed using a full endoscopic technique [17]. We report a case of cervical osteoid osteoma removal performed using the UBE technique.

A 50-year-old male patient visited the clinic with left-sided neck pain that had started 6 months ago. He had no radiating pain, and although he had taken medication and received injections at another hospital, his symptoms did not improve, so he visited Himplus hospital.

On the lateral x-ray, a radiolucent lesion about 1.5 cm in size was observed on the C3 lamina (Figure 1). On axial CT, a round low-attenuation nidus measuring approximately 15 mm in diameter is seen in the C3 lamina. It is accompanied by localized reactive sclerosis, without significant involvement of the spinal canal or neural foramen. (Figure 2). We also performed an MRI.

On contrast-enhanced T1-weighted fat-saturated images, the nidus shows marked enhancement, with the central area suspected of calcification remaining low signal. Surrounding bone marrow and soft-tissue edema areas also exhibit some enhancement (Figure 3).

Under suspicion of osteoid osteoma, we decided to proceed with surgery for diagnostic confirmation and excision. Although there are various methods, we chose to perform the surgery using a unilateral biportal endoscope because it is less invasive than open surgery, provides better visualization, minimizes structural damage, and allows for faster recovery.

The procedure consisted of the following steps:

Although diagnosis of osteoid osteoma is usually possible by clinical and imaging techniques, sometimes it is very difficult to distinguish between stress fracture or Brodie’s abscess and osteoid osteoma. Hence, there is often delay in diagnosis of this tumor [18]. In certain situations, a positive histological diagnosis can be helpful in confirmation of treatment method [19]. Surgery has remained to be the standard treatment in cases where the nature of lesion is in doubt [20]. Many options for surgical excision of spinal osteoid osteoma have been proposed: intralesional curettage, marginal or wide resection, and thermoablation including percutaneous RFA or laser coagulation [21]. Conventional procedures for open surgical excision often require paraspinal muscular detachment and facet disruption to perform complete resection of the nidus as the principle of treatment to achieve pain remission [22]. This affects spinal stability and necessitates spinal fusion and instrumentation, which is associated with increased blood loss, longer operative time and length of hospital stay, loss of spinal motion, and long-term complications including heterotopic ossification and adjacent segment disease [11,23,24].

The goal of surgery was to remove the nidus entirely without causing pathologic fracture, instability or disrupting the surrounding uninvolved tissues [25,26]. Regarding the choice of intervention, CT-guided RFA is frequently regarded as a first-line treatment for osteoid osteomas, particularly in long bones [27]. However, its application in the cervical spine poses specific challenges. The primary concern with RFA in the cervical region is the risk of thermal injury to neural structures, including the spinal cord and nerve roots, which lie in close proximity to the posterior elements. The narrow safety margin in the cervical spinal canal makes blind thermal ablation potentially hazardous [27,28]. Furthermore, the "heat-sink" effect of cerebrospinal fluid can occasionally lead to incomplete ablation [20].

To overcome these limitations, minimally invasive spine surgery has gained popularity. Minimally invasive procedures directly result in shorter hospitalization, shorter rehabilitation periods and decreased overall costs. Recently, endoscopic surgery has been highlighted as a "maximal benefit zone" for the cervical and thoracic spine, offering precise decompression while preserving structural integrity [29]. In this case, we employed the UBE technique. Unlike conventional open surgery, UBE utilizes 2 independent portals—one for the optical system and one for instruments—allowing for excellent visualization and free maneuverability. Park and Heo [30] described that UBE in the cervical spine allows for clear visualization of neural structures and safe bony resection with minimal soft-tissue trauma. The advantages of UBE are particularly evident in terms of postoperative pain and infection control. A recent meta-analysis by Lee et al. [31] reported that UBE posterior cervical foraminotomy resulted in favorable clinical outcomes with low complication rates. Because UBE involves muscle-splitting rather than detachment, postoperative muscle atrophy and pain are significantly reduced compared to open surgery [32,33]. Furthermore, the continuous saline irrigation system used during UBE plays a crucial role in infection control. It prevents temperature elevation from bone drilling, washes out debris and hematoma, and creates a clear operative field, thereby theoretically reducing the risk of surgical site infection compared to open or tubular approaches where dead space formation is more likely [31,34].

When comparing UBE with other minimally invasive techniques, such as tubular retractor systems, UBE offers distinct advantages for bone tumor resection. First, compared to the tubular retractor system, UBE offers a wider range of motion for instruments [35,36]. The tubular approach provides a restricted, tunnel-like view, which can make it challenging to access the full extent of a lesion without manipulating the tube and potentially damaging surrounding tissues. In contrast, UBE allows the surgeon to inspect the lesion from various angles without such restrictions [33,34].

In the present case, the tumor was located in the C3 lamina involving the facet joint. Our surgical priority was complete excision of the nidus while maintaining spinal stability. The UBE technique allowed us to precisely target the lesion with minimal necessary bone resection. Although a portion of the facet was resected to ensure complete tumor removal, the endoscopic approach enabled us to preserve the facet joint capsule and the lateral mass. This preservation of soft-tissue stabilizers and bony continuity resulted in immediate pain relief, and postoperative dynamic radiographs confirmed that spinal stability was maintained without the need for instrumentation.

UBE resection is an effective minimally invasive treatment for posterior cervical osteoid osteoma. It minimizes damage to surrounding soft tissue and bone. It is particularly advantageous over RFA in the cervical spine due to the elimination of thermal injury risks to neural structures. By offering superior visualization and ensuring continuous irrigation, UBE minimizes tissue and bone damage, reduces postoperative pain, and lowers infection risks compared to conventional methods.